In previously proposed arrangements for operations of this type, the workpieces are often inserted either singly or in batches on an indexing mechanism in a vacuum chamber, by a door therein. This is both time consuming and expensive since when each workpiece or batch is finished, it must be removed and replaced by fresh work which requires either elaborate sealing devices or means for raising the pressure in the chamber to atmospheric pressure whilst the replacement procedure is performed and the reduction of the pressure in the chamber is then again ready for the performance of the operation on the fresh work therein.
To avoid this problem, it is necessary to transfer the workpieces through a sealed chamber on a continuous basis conveniently in a series of individual workpiece compartments which move along an input passage and into the sealed chamber in which the pressure is reduced, and then out of the chamber along an output passage, each compartment being sealable whilst in the input and output passages so that the pressure in the individual compartments can be independently varied as necessary, i.e. to reduce the pressure in a compartment before it reaches the sealed chamber and thereby avoid fluctuations in the reduced pressure in the sealed chamber. However, previous attempts to provide such a system tend to be inefficient, requiring either complex sealing arrangements or a compromise in the effectiveness of the seals of each compartment.
The object of the present invention is to provide an improved apparatus and method for transferring work on a continuous basis through a region of reduced pressure having efficient seals of simple construction.